Development of advanced radiation detectors is aimed at high energy-resolution detectors that are capable of reliable and long term non-degrading operation at elevated temperatures under high doses of ionizing radiation. Such detectors can be built on silicon carbide (SiC), a wide band-gap semiconductor, which has been recognized for long time as an attractive alternative to more mature technologies in intense and rugged environments.
Silicon carbide (SiC), a wide band-gap semiconductor, has been recognized for high-power, high frequency, and high-temperature opto-electronics applications. Over the past decade, SiC has developed significantly in the area of high power electronics, making high-quality SiC material increasingly available for research and development and other commercial applications. This gained momentum to the development of SiC based ionizing radiation detectors, where a defect-free high purity single crystals and thick epitaxial layers are crucial for high resolution, high sensitivity, and low noise detectors of x-rays, gamma-rays, and low-energy ionizing radiation. Detectors based on 4H—SiC epitaxial layers with low level of impurities and defects can reliably detect any type of ionizing radiation at high radiation background at elevated temperatures and can be used in radiation doses as high as 22 MGy. Diode-type detectors fabricated using SiC epitaxial layers perform well in high-resolution detection of low penetration depth α-radiation, whereas the resolution of the detectors based on bulk semi-insulating SiC grown by physical vapor transport (PVT) is not yet adequate presumably due to high density of defects and deep level centers, implying that further quality improvement of these crystals is necessary.
The present inventors have evaluated the state-of-the-art n-type 4H—SiC epitaxial layers in terms of quality and electrical and defect properties. It was found that there is no commercially available detector that is sensitive enough to soft x-rays in the sub-keV to 10 key spectral range. As such, there exists a need in the art for improved detectors, particularly in the soft x-rays and gamma range spectral ranges.
The prospect of SiC Schottky diodes as alpha particle detectors was first reported by Babcock and co-workers. Ruddy et al., reported a resolution of 5.8% (full width at half maxima, FWHM) at a deposited energy of 294 keV and 6.6% (FWHM) at a deposited energy of 260 keV by alpha particles from a collimated 238Pu source in 4H—SiC Schottky diodes with circular contacts of diameter 200 and 400 μm. F. Nava et al. reported very robust 5.48 MeV alpha particle signal in 4H—SiC epitaxial detectors with circular contacts of ˜2 mm diameter. However, they have not achieved a saturation of the charge collection efficiency even at a bias voltage of 200 V. In a later work, Ruddy et al. reported an energy resolution of 5.7% for a deposited energy of 89.5 keV alpha particles from a 100 μm collimated 148Gd source in similar detectors with relatively larger Schottky contact diameter of 2.5, 3.5, 4.5 and 6.0 mm and 10 μm thick epilayer. Among high resolution alpha particle detection reports, Ruddy et al. reported fabrication of alpha particle detectors with aluminum guard ring structures using which they obtained an energy resolution close to 46 keV for alpha particles from a 238Pu source and 41.5 keV for alpha particles from a 148Ga source. Ivanov et al. reported an energy resolution of 20 keV in the energy range 5.4-5.5 MeV. In another work, Ruddy et al. reported an energy resolution of 20.6 keV for 238Pu alpha particles and Pullia et al. reported 0.9% energy resolution in the 4.8-5.8 MeV energy range at a temperature of 55° C. using a SiC/GaN detector with a 1000 Å Au entrance window. However, there exists a need in the art for improved alpha particle detectors.